1. Field of the Invention
The present invention relates to an apparatus for reducing the risk of damage to buildings as a result of lateral forces applied to the building and, in particular, concerns a pre-assembled internal shear panel that can be installed into a building wall to reduce the risk of the building wall becoming dislodged from the foundation as a result of lateral forces such as those generated in earthquakes and high winds.
2. Description of the Related Art
In typical building construction the walls are comprised of a frame that is anchored to the foundation and a covering that is installed onto the frame. Typically, the frame of a building has a number of vertically extending studs that are positioned between an upper and a lower plate. The lower plate is typically anchored to the foundation and the covering material, e.g., plywood, siding and the like, is then nailed to the studs.
One problem that occurs in buildings is that lateral forces applied in a direction parallel to, and in the plane of, the wall can cause the upper section of the wall to move relative to the lower plate which is anchored to the foundation. These forces often occur as a result of natural phenomenon such as high winds and earthquakes. It will be evident that too much movement of the upper sections of the wall relative to the anchored lower plate can result in damage to the frame of the wall which can further result in the wall collapsing.
To address this particular problem, buildings are often equipped with a lateral bracing system. One type of lateral bracing system is known as shear panels that are installed in the walls to stiffen the structure against racking or deformation in the plane the walls. For example, in the typical residential building, wherein the frames are primarily constructed of wood, plywood sheathing is attached to three or more of the studs, and to the upper and lower plate of the wall, to inhibit the movement of the upper portion of the wall in response to these lateral forces. Specifically, the end studs of the shear panel or posts are typically fastened to a heavier anchor bolt, known as a holdown bolt, at a position adjacent to the end posts by means of various hardware types known as holdowns. The plywood, which forms a vertical diaphragm, is attached to the upper plate and the lower plate of the wall, and also to the posts with specified boundary fasteners such that the shear force is transmitted through the diaphragm to end posts, the holdown device, and bolt. Hence, the tendency of the upper portion of the wall to move relative the lower portion of the wall as a result of the shear forces is reduced. Basically, the plywood diaphragm creates diagonal braces that inhibit movement of the upper portion of the wall relative to the lower portion.
These shear panels are typically built in the field during the construction of the building. It will be appreciated that constructing these structures in the field can be time consuming and can also result in construction errors that will affect the strength of the wall.
Further, these types of shear panels and, in particular, the plywood shear panels used in wooden framed buildings, must be comparatively large to withstand the significant amount of lateral forces that are generated in large earthquakes. For example, most building codes limit the story drift or lateral deformation to ¼″ for an 8′ wall height in all types of buildings. The ratio of the height of various shear panels to their width is also limited by the building code depending on the type of sheathing material used. To achieve this limitation on story drift in response to this applied lateral force, the shear panel must generally include a plywood diaphragm that is on the order of 2 to 4 feet in length. While on long walls there may be the space available between openings to position a 4-foot long or greater shear panel, in smaller buildings with smaller lengths of walls, there is often no room to construct a shear panel of this size. Further, it will be appreciated that multiple story buildings are more susceptible to larger lateral forces often necessitating even larger lateral bracing structures. This exacerbates the problem of a limited amount of space in walls of smaller lengths.
Hence, there is a need for a shear panel which is easy to install and is comparatively small in size so that it can be readily installed in walls having shorter lengths. To this end, there is a need for a prefabricated shear panel that is capable of ready installation into and between the studs of walls wherein the shear panel is capable of minimizing the movement of the upper portion of the wall relative to the lower portion to within an acceptable amount.